Catalytic composition for the polymerization of olefins and its process of preparation

ABSTRACT

Process for the preparation of a catalytic composition for the polymerization of olefins. At least partial electrochemical oxidation of aluminum in a solvent of α,ω-dihalogeno-alkane and simultaneously the electrochemical reduction of a compound of titanium (IV) occur in process. 
     The catalytic composition comprises at least one titanium compound, at least one halogenated organo-aluminum compound and at least one inorganic magnesium compound in suspension in at least one α,ω-dihalogeno-alkane. The titanium compound is essentially a titanium (III) compound. The overall content of titanium (II) and titanium (IV) is less than or equal to 15% of the total titanium content.

BACKGROUND OF THE INVENTION

The present invention concerns a process for the preparation, by anelectrochemical route, of a catalytic composition for the polymerizationof olefins, a catalytic composition for this polymerization, and anapplication of the catalytic composition to the polymerization ofolefins More particularly, the present invention relates to thepolymerization of ethylene and the copolymerization of ethylene with atleast one α-olefin.

Means of obtaining catalysts containing at least one derivative of atransition metal, also known as "Ziegler-Natta catalysts," and their usefor the polymerization of a α-olefins have been known for a long time.Those skilled in the art have sought ceaselessly to improve thesecatalysts to increase their catalytic activity and/or influence thecharacteristics of the polymers obtained.

Work has also been carried out with the object of using Ziegler-Nattacatalysts under high temperature conditions to permit a shorter contacttime between the olefin to be polymerized and the catalyst. This wouldresult in an increase of the productivity of the installations. Thecatalyst must, therefore, have a high stability which is compatible withthese drastic conditions of polymerization as well as a high activityand a high initial rate of polymerization.

Increasing the catalytic activity of Ziegler-Natta catalysts is aconstant preoccupation which aims simultaneously, by the utilization ofsmaller quantities of catalyst, to reduce the manufacturing cost of thepolymer and to obtain polymers in which the level of catalytic residuesis as low as possible. The latter objective has primarily the purpose ofavoiding purification of the polymers and of obtaining, withoutpurification, polymers which have no tendency to degrade mechanicallyand/or thermally, during or after conversion into finished products.

It is known from another source that compounds of titanium of valency IIare very slightly active in Ziegler-Natta catalysis. Many titaniumcompounds exist at the maximum valency (IV) and their reduction leads tomixtures of compounds of titanium (III) and of titanium (II) whichbecome less active as the level of titanium (II) increases. One problemin the improvement of Ziegler-Natta catalysts is, therefore, to obtain,by reduction of compounds of titanium (IV), compounds of titanium (III)essentially exclusive of compounds of titanium (II).

The applicant has now found that it is possible to resolve this problemby means of a new process for the reduction of compounds of titanium(IV). The catalytic compositions obtained by this process have a veryhigh activity regardless of the conditions of polymerization.

It is known to prepare components of Ziegler-Natta catalysts by anelectrochemical route. For example, U.S. Pat. No. 3,787,383 describes anelectrolytic process for preparing certain bis(metal halide)methanes,such as bis(dichloroaluminum)methane Cl₂ AlCH₂ AlCl₂. By this process,an electrolyte of formula HOAlCl₂ is electrolysed in the presence of amethylene dihalide, such as CH₂ Cl₂, or a gem-dihalide between analuminum anode and a cathode of the same metal or of an inert material,such as platinum or carbon. A derivative of a transition metal is addedto the resulting activator to obtain the catalytic system. Thistransition metal derivative does not undergo reduction.

It is also known from U.S. Pat. No. 3,546,083 to prepare simultaneouslythe two components (catalyst and activator) of the catalytic system byelectrolysis of a medium containing a methylene dihalide and anelectrolyte, such as HOAlCl₂. The anode is constituted by a transitionmetal associated with aluminum and the cathode, which is not consumedduring electrolysis, is a metal or graphite The preparation of thetransition metal compound, therefore, takes place by oxidation of themetallic anode. It is not specified in what valency state the transitionmetal is found in the compound formed.

SUMMARY OF THE INVENTION

The applicant has now found that it is possible to prepare the twocomponents of the catalytic system simultaneously by electrolysing adihalogenated compound in the presence of an anode containing aluminum(preparation of the activator) and simultaneously reducing a compound oftitanium (IV) at the cathode (preparation of the catalyst).

More specifically, the present invention provides a process for thepreparation of a catalytic composition for the polymerization ofolefins. That process comprises at least partial electrochemicaloxidation of aluminum in a halogenated solvent of theα,ω-dihalogenalkane type and simultaneously the electrochemicalreduction of a compound of titanium (IV).

These and other features and advantages of the present invention will bemade more apparent from the following description of the preferredembodiment.

DESCRIPTION OF THE DRAWING

FIG. No. 1 is an electrolytic cell for preparing catalytic compositionsof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The α,ω-dihalogenoalkane has the general formula X-(CH₂)_(n) -X' inwhich X and X', which may be identical or different, are each a halogenatom, such as chlorine, bromine and fluorine, and n is an integerbetween 1 and 10, preferably between 1 and 6. The nature of the halogenatoms and the value of n are such that the α,ω-dihalogenalkane is liquidunder normal conditions of temperature and pressure. Among the compoundscorresponding to the preceding general formula, dichloromethane,1,2-dichloroethane and 1,4-dichlorobutane or their mixtures areadvantageously chosen.

To reduce the quantity of halogenated solvent while preserving the sameconcentration of titanium (IV) compound, it is preferred to carry outthe simultaneous electrochemical oxidation and reduction in theadditional presence of an inert solvent. This solvent is preferablychosen from the saturated aliphatic or cycloaliphatic hydrocarbonshaving from 6 to 14 carbon atoms, whose boiling point, at atmosphericpressure, is not lower than 60° C., and their mixtures. It could be, forexample, a cut of C₁₀ -C₁₂ saturated aliphatic hydrocarbons. The inertsolvent is used in a quantity which can be up to 100 parts by weight,per 100 parts by weight of the halogenated solvent.

The simultaneous electrochemical oxidation and electrochemical reductionpreferably take place in an electrolytic cell by passing an electriccurrent between an anode and a cathode which are immersed in theelectrolyte containing the halogenated solvent, if necessary with theaddition of an inert solvent, and the compound of titanium (IV). Byreason of its constitution, this electrolyte is a poor conductor;however, it is possible to increase its conductivity by adding to itquantities, which may be up to 10 times the quantity of the titanium(IV) compound (expressed in moles), of at least one higher olefin. Forthis purpose, an α-olefin having, for example, from 4 to 16 carbonatoms, preferably hex-1-ene, may be used.

The process according to the invention is carried out at a temperatureof between 0° C. and the boiling point of the solvent (halogenated and,if necessary, inert) or that of the α-olefin. Since the electrolysis isexothermic, a means of cooling the reaction medium is to be providedtogether with, if necessary, an electrolytic cell which is capable offunctioning under slight over-pressure (up to about 2 bars).

The titanium (IV) compound subjected to electrochemical reduction ischosen from the compounds of general formula Ti(OR)_(n) X_(4-n) in whichX is a halogen atom chosen from fluorine, chlorine, bromine and iodine;R is an alkyl radical having from 1 to 10 carbon atoms; and 0≦n≦4.Preferably, the titanium (IV) compound is titanium tetrachloride,diethoxytitanium dichloride or di(n)butoxytitanium dichloride. Theconcentration of the titanium (IV) compound in the reaction medium isadvantageously between 20 and 600 millimoles per liter. Although a highconcentration leads to conductivity problems and problems with diffusionof the species in a medium whose viscosity has been increased, it does,on the other hand, permit the molar ratio halogenated solvent/ titaniumin the catalyst obtained to be reduced and, thus, the drawbacks of thepresence of too large a quantity of the halogenated compound duringpolymerization is avoided.

According to a variant of the process of the present invention, it ispossible to add a vanadium (IV) or vanadium (V) compound, chosen fromthe compounds of general formula VO(OR)_(m) X_(3-m) in which X is ahalogen; R is an alkyl radical having from 1 to 6 carbon atoms; and0<m<3, and the compounds of formula VX₄, in which X is a halogen, to thereaction medium during electrolysis. Examples of such compounds are VCl₄and VOCl₃. The concentration of the vanadium compound in the reactionmedium is advantageously between 0 and 100 millimoles per liter.

Analyses carried out on the reaction mixture after the electrochemicaloxido-reduction under various conditions have shown that, in asurprising manner, whatever quantity of electricity has passed throughthe reaction medium, the titanium (IV) derivative was not reduced beyondthe (III) degree of oxidation. It has thus been found that it ispossible to pass the quantity of current necessary to generate thehalogenated organoaluminum compound without modifying the degree ofoxidation of the titanium (III) compound obtained. Simultaneouselectrochemical oxidation and electrochemical reduction are thus, in anadvantageous manner, carried out by passing a quantity of electricity ofbetween 1 and 12 Faradays per mole of titanium, and, preferably, between1 and 8 Faradays per mole of titanium, through the reaction medium.

The invention can be carried out according to the three routes which arewell known to electrochemists: with an imposed cathodic potential, witha regulated cathodic potential or at constant current.

Electrochemical oxido-reduction with an imposed cathodic potential iscarried out with an apparatus comprising a reference electrode (forexample Ag/AgCl/Cl), a working electrode (cathode) and a solublealuminum auxiliary electrode (anode). A constant potential is imposedbetween the reference electrode and the cathode. The voltage regulatorconnected between cathode and anode then delivers the working voltage.The constant potential imposed is between -0.5 and -1 volt.

The regulated cathodic potential route establishes a given workingvoltage between the cathode and the anode without using a referenceelectrode. It has been established that these reactions (solubilizationof the aluminum anode and reaction with the halogenated solvent,reduction of the titanium (IV) derivative at the cathode) are possiblewithout the titanium (III) derivative obtained being further reduced atthe cathode. The process can therefore be carried out at a regulatedcathodic potential of between 20 and 200 volts Passing an initialFaraday per mole of titanium reduces the titanium (IV) derivative to atitanium (III) derivative and produces, per gram-atom of titanium, 1gram-equivalent of aluminum in the form of a halogenated organoaluminumderivative. The passage of the following Faradays allows the quantity ofthe halogenated organoaluminum derivative to be increased withoutreduction of the titanium (III) compound formed.

Constant current oxido-reduction predetermines the value of the currentwhich will travel through the electrolyte and uses a regulatoryapparatus instantaneously to deduce the value of the potentialdifference to be applied between the anode and the cathode to maintainthe current at the chosen value. According to this route, theelectrolysis is carried out advantageously for the present invention ata current of between 100 mA and 100 A.

The process according to the invention is carried out in an electrolyticcell whose cathode is made of a metal (generally a metallic basket)chosen in particular from platinum, iron, aluminum and their respectivealloys. The cathode can be the electrolytic cell itself, which is thenmade of metal. The aluminum or aluminum-based alloy anode is thereforelocated near the internal wall of the cell. If anode and cathode areboth aluminum or aluminum alloy, it is then possible to carry out theelectrolysis using alternating current.

The reaction medium obtained after electrolysis may be used as acatalyst for the polymerization of olefins. It may also be used in thepresence of at least one organoaluminum activator such as, for example,trialkyl aluminum, aluminoxane, siloxane or siloxalane. The catalyticyields observed are satisfactory.

It is moreover possible to improve the performances of the catalyticcompositions thus obtained by adding a support such as, for example, amagnesium halide Two routes are thus possible and consist either incarrying out the simultaneous electrochemical oxidation and theelectrochemical reduction in the presence of the magnesium halide or,preferably, in adding the magnesium halide to the reaction medium afterelectrolysis. In both cases, the atomic ratio Mg/Ti is advantageouslyless than or equal to 15.

Moreover, although dialkyl magnesium compounds are powerful reducingagents, it has surprisingly been found that their addition to thereaction medium after electrolysis allows nascent magnesium halide to beformed without appreciable reduction of the titanium (III) compoundformed According to this third route, at least one organo-magnesiumderivative of formula R-Mg-R', in which R and R' are alkyl radicalswhich may be identical or different and have from 1 to 12 carbon atoms,is added to the reaction medium, after electrolysis, to obtain an atomicratio Mg/Ti of up to 15. The organo-magnesium derivative is chosen, forexample, from n-butylethyl- magnesium, n-butyl-s-butyl magnesium,di-n-hexyl magnesium and n-butyl-n-octyl magnesium.

The activity of the catalytic compositions according to the inventionmay also be improved by adding to the reaction medium, afterelectrolysis, at least one vanadium (III), (IV) or (V) compound in amolar ratio V/Ti of up to 6, corresponds to the general formulaindicated above. It may be added to the reaction medium in solution inan inert solvent such as a saturated hydrocarbon having from 6 to 12carbon atoms, for example a cut of C₁₀ -C₁₂ saturated aliphatichydrocarbons.

A further subject of the present invention is a catalytic compositionfor the polymerization of olefins comprising at least one titaniumcompound and at least one halogenated organo-aluminum compound insuspension in at least one α,ω-dihalogenoalkane. In this composition,the titanium compound is essentially a titanium (III) compound and theoverall content of titanium (II) and titanium (IV) is less than or equalto 15% of the total titanium content. The composition also contains inaddition at least one inorganic magnesium compound in suspension.

The halogenated organo-aluminum compound has the general formula X₂Al(CH₂)_(n) AlX₂ in which X is a halogen, preferably chlorine, and n isbetween 1 and 10.

The catalytic composition may also contain an inert solvent. Theα,ω-dihalogenoalkane and the inert solvent have the definitions alreadydescribed above.

The oxidation state of the titanium compound is determined by redoxtitration in three parts, the first allowing the calculation of Ti²⁺+Ti³⁺, the second 2Ti²⁺ +Ti³⁺, the content of valency II titaniumcompounds being therefore obtained by difference, and the third Ti²⁺+Ti³⁺ +Ti⁴⁺ (total quantity of titanium which permits the content ofTi⁴⁺ compounds to be deduced). The method used is described in detailbelow Generally the content of tetravelent titanium derivatives is verylow, or even undetectable. The content of divalent derivative isgenerally low, for example, less than 2 mol %.

By inorganic magnesium compound is understood a magnesium salt of amineral acid, such as a halide, advantageously magnesium chloride,preferably in the anhydrous form. The inorganic magnesium compound maybe formed in situ during the preparation of the catalytic composition,for example by reaction between a magnesium derivative and thehalogenated derivatives present in the electrolyte.

The catalytic composition may also contain at least one vanadiumcompound, advantageously with valency III, such as the chloride VCl₃.

In the catalytic composition according to the invention, the followingatomic ratios are advantageously chosen: Cl/Ti between 10 and 180,preferably between 20 and 60; Al/Ti between 0.5 and 12, preferablybetween 3 and 6; Mg/Ti between 1 and 15, preferably between 3 and 8; andV/Ti between 0 and 6, preferably between 0 and 3.

The catalytic composition according to the invention may in additioncontain at least one α-olefin having, for example, from 4 to 16 carbonatoms, possibly in the at least partially polymerized state.

The catalytic composition may be prepared, for example, by mixing theconstituents, it being possible to prepare the halogenatedorgano-aluminum compound according to the teaching of U.S. Pat. No.3,787,383. It is advantageously prepared according to the processdescribed above including the supplementary step of the addition ofmagnesium halide, before or after electrolysis Alternatively, anorgano-magnesium derivative is added after electrolysis, which allowsthe magnesium halide to be obtained in situ.

This catalytic composition may be used for the polymerization. Thecatalytic composition includes at least one activator comprising atleast one organo-metallic derivative of groups I to III of the periodclassification of the elements. The organometallic derivative is,preferably, an organo-aluminum derivative. The quantity of theorgano-metallic derivative is such that the atomic ratioAl(added)/Ti(+V) may be up to 100.

The activator is advantageously chosen from the trialkyl aluminumcompounds AlR₃, the tetraalkyl aluminoxanes RR'Al-O-AlR"R'", themono-alkyl-silanolatodialkyl aluminum compounds R-SiH₂ -O-AlR'R" andtheir mixtures, the alkyl radicals R, R', R", R'", which may beidentical or different, having from 1 to 12 carbon atoms One may cite,for example, triethyl aluminum, tri-n-butyl aluminum, tri-octylaluminum, tetra-iso-butyl aluminoxane and methyl-silanolato-di-isobutylaluminum.

A further subject of the present invention is also a process for thepolymerization of olefins, at a temperature of between 20 and about 350°C., in the presence of a catalytic composition such as described above.The olefins which may be polymerized according to this procedureinclude, in particular, ethylene and the α-olefins having from 3 to 6carbon atoms, such as propylene, but1-ene and 4-methylpent-1-ene.Ethylene may also be copolymerized with α-olefins having from 3 to 12carbon atoms, such as, as well as those which have already been cited,hex-1-ene and oct-1-ene.

The polymerization or the copolymerization may be carried out accordingto a continuous or discontinuous process, in an autoclave reactor or atube reactor.

The polymerization of ethylene, alone or with at least one α-olefin, maybe carried out at a temperature of between 20° C. and 250° C., under apressure of up to about 200 bars, in solution or in suspension in aninert hydrocarbon having at least 6 carbon atoms, such as a cut of C₁₀-C₁₂ saturated aliphatic hydrocarbons. The concentration of titaniumderivative in the catalytic composition of the Ziegler type isadvantageously between 100 and 400 millimoles per liter.

It may also be carried out, in a continuous manner, in a reactor inwhich the mean residence time of the catalytic composition is between 1and 150 seconds, and at a temperature of between 160° and 350° C. undera pressure of between 400 and 3,000 bars.

The molecular weight of the polymers obtained may be adjusted bycarrying out the polymerization or the copolymerization in the presenceof up to 2 mole % of a chain transfer agent, such as hydrogen.

The following examples are given with the intention of illustrating theinvention without limiting it.

EXAMPLES 1 TO 17 Preparation of the Catalytic Composition

The catalytic composition is prepared in an electrolytic cellrepresented schematically in FIG. 1. The body of the cell (1) isprovided with a double jacket (2) allowing the temperature to becontrolled. The anode (3) and the cathode (4) are cylindrical andcoaxial. The reaction medium is magnetically stirred by means of the bar(5). The catalytic compositions are prepared under an inert atmosphere.

During the preparation of catalytic compositions according to thevariant using an imposed cathodic potential, the electrolysis is carriedout with the aid of a voltage regulator supplying a voltage E such thatE=V_(A) -V_(C) +RI, where V_(A) is the anodic potential, V_(C) thecathodic potential imposed with the aid of the voltage regulator, and RIthe voltage drop which represents the larger part of the voltage E to beapplied. The apparatus, therefore, comprises three electrodes:

(1) a Ag/AgCl/Cl⁻ reference electrode whose chlorine ion is provided bya 0.02 mole/liter solution of tetra-butylammonium chloride;

(2) a cathode (platinum basket) maintained at a voltage V_(C) withrespect to the reference electrode; and

(3) an anode in the form of an aluminum cylinder.

The reference electrode is situated near the cathode. Weighing the anodebefore and after electrolysis allows the calculation, by difference, ofthe quantity of aluminum consumed, and therefore combines with thechlorinated solvent to form the chlorinated organo-aluminum compound.

The amount of electricity which has travelled through the electrolyte ismeasured by means of an integrator placed in series in the anode circuitor the cathode circuit.

During preparation of catalytic compositions according to the variantusing a regulated cathodic potential, the electrolysis is carried out byapplying a constant voltage V_(A) -V_(C), expressed in volts, between:

an aluminum anode; and

a cathode, generally a platinum basket.

A potential difference is imposed between the anode and the cathode.

Table I summarizes the conditions used. In all these experiments:

(i) the quantity of halogenated solvent was 35 ml;

(ii) the anode was an aluminum cylinder;

(iii) the reference electrode (in the experiments conducted with animposed cathodic potential) was a Ag/AgCl/Cl⁻ electrode;

(iv) the cathode voltage with respect to the reference electrode (in theexperiments using an imposed cathodic potential) was -0.5 volt;

(v) the temperature was 35° C.; and

(vi) nitrogen was used as the inert atmosphere.

The following abbreviations indicate:

SX: the nature of the halogenated solvent used:

DCM is dichloromethane ClCH₂ Cl

DCE is 1,2-dichloroethane Cl-CH₂ -CH₂ -Cl.

[TiCl₄ ]: is the concentration of TiCl₄, in millimoles per liter, in thehalogenated solvent.

CA: the conductivity additive used, with, between brackets, the molarratio conductivity additive/ TiCl₄.

V_(A) -V_(C) : the voltage between the anode and the cathode, for theexperiments using regulated cathodic potential.

t: the electrolysis time in minutes.

F: the number of Faradays which have travelled through the electrolyteat the end of the preparation, per mole of titanium.

                  TABLE I                                                         ______________________________________                                        Electrolysis Using Imposed Cathodic Potential                                 Example                                                                              SX      [TiCl.sub.4 ]                                                                           CA        t      F                                   ______________________________________                                        1      DCM     28.6       --       300    1                                   2      DCM     28.6      Hex-l-ene (8)                                                                            70    1                                   3      DCE     28.6      Hex-l-ene (8)                                                                            55    1                                   4      DCE*    28.6      Hex-l-ene (8)                                                                           300    1                                   5      DCE     28.6      Hex-l-ene (8)                                                                           135    3                                   6      DCE     143       Hex-l-ene (1.6)                                                                         750    1                                   7      DCE     286       Hex-l-ene (0.8)                                                                         1200   3                                   8      DCM     28.6 +    Hex-l-ene (8)                                                                           130    1                                                  VOCl.sub.3 28.6                                                ______________________________________                                         *DCE: 17.5 ml + cut of C.sub.10 -C.sub.12 saturated hydrocarbons (inert       solvent): 17.5 ml.                                                       

    ______________________________________                                        Electrolysis at Regulated Voltage                                             (Halogenated Solvent: DCE)                                                                     CA                                                           Example [TiCl.sub.4 ]                                                                          (hex-l-ene)                                                                             Cathode V.sub.A -V.sub.C                                                                     F                                   ______________________________________                                         9      286      (0.8)     Pt      20     3                                   10      28.6     (8)       Pt      50     3                                   11      572      (0.4)     Pt      50     3                                   12      286      (0.8)     Pt      50     5                                   13      286      (0.8)     Pt      50     6                                   14      286      (0.8)     Pt      50     8                                   15      286      (0.8)     Pt      70     3                                   16      28.6     (8)       Al      50     3                                   17      28.6     (8)       Steel   50     3                                   ______________________________________                                    

EXAMPLES 18 TO 43 Modification of the Catalytic Compositions EXAMPLE 18

To the catalytic composition obtained in Example 1 is added a quantityof vanadium oxytrichloride (VOCl₃) such that the atomic ratio V/Ti inthe modified catalyst is equal to 1.

EXAMPLE 19

To the catalytic composition obtained in Example 3 is added a quantityof VOCl₃ such that the atomic ratio V/Ti in the modified catalyst isequal to 1.

EXAMPLE 20

To the catalytic composition obtained in Example 2 is added a quantityof finely ground MgCl₂ such that the atomic ratio Mg/Ti in the modifiedcatalytic composition is equal to 6.

EXAMPLE 21

To the catalytic composition obtained in Example 2 is added a quantityof n-butyl ethyl magnesium such that the atomic ratio Mg/ Ti in themodified catalytic composition is equal to 7.

EXAMPLE 22

The same process as in Example 21 is repeated using the catalyticcomposition obtained in Example 3 as the starting material. The Mg/Tiratio is equal to 6.5.

EXAMPLE 23

To the catalytic composition obtained in Example 18 is added a quantityof n-butyl ethyl magnesium such that the atomic ratio Mg/Ti is equal to6.

EXAMPLE 24

To the catalytic composition obtained in Example 3 are added a quantityof VOCl₃ such that the atomic ratio V/Ti is equal to 1. Then, a quantityof n-butyl ethyl magnesium is added such that the atomic ratio Mg/Ti isequal to 6.5.

EXAMPLE 25

The process in Example 24 is repeated in totality on the catalyticcomposition obtained in Example 4.

EXAMPLE 26

The process in Example 24 is repeated in totality on the catalyticcomposition obtained in Example 5.

EXAMPLE 27

To the catalytic composition obtained in Example 5 are added first aquantity of n-butyl ethyl magnesium such that the atomic ratio Mg/Ti isequal to 6, then a quantity of VOCl₃ such that the atomic ratio V/Ti isequal to 1.

EXAMPLES 28 TO 39

The process in Example 27 is repeated in totality on, respectively, thecatalytic compositions obtained in Examples 4, 6, 7, 11, 10, 16, 17, 9,12, 13, 14, and 15.

EXAMPLE 40

To the catalytic composition obtained in Example 10 are addedsuccessively sufficient vanadyl tri(iso-butylate)(VO(C₄ H₉ O)₃) toobtain an atomic ratio V/Ti equal to 1. Then, sufficient n-butyl ethylmagnesium is added to obtain an atomic ratio Mg/Ti equal to 6.

EXAMPLE 41

The operating method of Example 10 was repeated, replacing TiCl₄ withTi(OC₄ H₉)₂ Cl₂.

EXAMPLE 42

To the catalytic composition obtained in Example 41 was added n-butylethyl magnesium in a quantity such that the atomic ratio Mg/Ti is equalto 6.

EXAMPLE 43

The operating method of Example 13 was repeated using a steelelectrolytic cell, whose trough was used as the cathode. The anode is analuminum plate placed a small distance from the internal wall of thecell. After the passage of 3 Faradays per mole of titanium under avoltage V_(A) -V_(C) of 50 volts, n-butyl ethyl magnesium is added tothe catalytic composition obtained until an atomic ratio Mg/Ti equal to6 is obtained. Then, VOCl₃ is added until an atomic ratio V/Ti equal to1 is obtained.

EXAMPLES 44 TO 63 Homopolymerization of Ethylene at 80° C.

600 ml of a cut of C₁₀ -C₁₂ saturated aliphatic hydrocarbons then aquantity of triethyl aluminum such that the ratio Al/Ti afterintroduction of the catalytic composition will be equal to 100, areintroduced into a stirred reactor, maintained at 80° C. by means of awater-bath. The apparatus is purged with nitrogen and then saturatedwith ethylene up to a pressure of 1.1 bar. The required quantity of thecatalytic composition is then injected. After one hour, 20 ml of ethanolare added to stop the polymerization. The polyethylene obtained iscollected and then separated off, washed, dried and weighed. Thecatalytic yield (R_(c)) is expressed in groups of polyethylene formedper millimole of titanium, or of titanium+vanadium as appropriate, perhour.

The results obtained are given in Table II.

                  TABLE II                                                        ______________________________________                                                       Catalytic                                                                     composition                                                    Example        of example                                                                              R.sub.c                                              ______________________________________                                        44              1         125                                                 45              2         150                                                 46              5         290                                                 47              8         215                                                 48             10         300                                                 49             41         266                                                 50             18         790                                                 51             19         460                                                 52             20         205                                                 53             21         520                                                 54             22        1335                                                 55             23        1035                                                 56             24        1710                                                 57             26        2185                                                 58             32        1165                                                 59             33        1260                                                 60             34        1240                                                 61             40        1383                                                 62             42        2080                                                 63             43        1280                                                 ______________________________________                                    

EXAMPLES 64 to 81 Homopolymerization of Ethylene at 200° C.

600 ml of a cut of C₁₀ -C₁₂ saturated hydrocarbons are introduced intoan autoclave reactor with a capacity of 1 liter and provided with meansof stirring and of temperature regulation. The apparatus is purged withnitrogen while raising the temperature to 200° C. 0.1 millimole(expressed as Ti+V) of the catalytic composition are then introduced,followed by the activator and ethylene up to a pressure of 6 bars, whichpressure is maintained for 1 minute.

The contents of the reactor are then discharged and the polymer isseparated off, washed, dried and weighed. The quantity (Q) obtained isexpressed as grams per gram-milliatom of transition metal per minute permole 1⁻¹ of ethylene.

The catalytic composition used (no. of the example in which itspreparation is described), the nature of the activator, the atomic ratioAl (in the activator)/Ti (or Ti+V) (in the catalytic composition) andthe quantity (Q) of polyethylene obtained are given in Table III. Theactivators used are shown by:

TEA: triethyl aluminum;

TiBAO: tetra-iso-butyl aluminoxane; and

Siloxal H₂ methyl-silanolato-di-isobutyl aluminum.

The ratios of activators indicated in brackets are molar ratios.

                  TABLE III                                                       ______________________________________                                               Catalyst                 Al/Ti                                                according                (or Al/                                       Example                                                                              to Example                                                                              Activator      Ti + V) Q                                     ______________________________________                                        64     24        TEA            10       290                                  65     25        TEA            10       355                                  66     28        TEA            10       435                                  67     28        TiBAO          10       585                                  68     28        TiBAO          20       575                                  69     28        SILOXAL H.sub.2                                                                              20       570                                  70     28        TiBAO/SILOXAL H.sub.2                                                                        20       810                                                   (0.5/0.5)                                                    71     27        TiBAO/SILOXAL H.sub.2                                                                        20       925                                                   (0.5/0.5)                                                    72     29        TiBAO/SILOXAL H.sub.2                                                                        20       890                                                   (0.5/0.5)                                                    73     29        TEA/SILOXAL H.sub.2                                                                          20       960                                                   (0.35/0.65)                                                  74     30        TiBAO/SILOXAL H.sub.2                                                                        20      1220                                                   (0.5/0.5)                                                    75     30        TEA/SILOXAL H.sub.2                                                                          20      1310                                                   (0.25/0.75)                                                  76     31        TEA/SILOXAL H.sub.2                                                                          20      1395                                                   (0.25/0.75)                                                  77     35        TEA/SILOXAL H.sub.2                                                                          20      1060                                                   (0.25/0.75)                                                  78     36        TEA/SILOXAL H.sub.2                                                                          20      1250                                                   (0.25/0.75)                                                  79     37        TEA/SILOXAL H.sub.2                                                                          20      1120                                                   (0.25/0.75)                                                  80     38        TEA/SILOXAL H.sub.2                                                                          20      1170                                                   (0.25/0.75)                                                  81     39        TEA/SILOXAL H.sub.2                                                                          20      1505                                                   (0.25/0.75)                                                  ______________________________________                                    

EXAMPLES 82 to 89 Copolymerization of Ethylene With at Least Oneα-Olefin at 200°-260° C.

The polymerization installation functions continuously and comprises astirred, temperature-controlled autoclave reactor, fed with a mixture ofethylene and α-olefin by means of 2 compressors arranged in series. Thesecond compressor receives in addition the monomers which have notreacted and which come form a separator into which the product from thereactor flows continuously. The separator is placed immediatelydownstream of an expansion valve situated at the exit from the reactorand is held at a pressure of about 250 bars. The polymer collected fromthe bottom of the separator is introduced, via an expansion valve, intoa hopper from where the polymer, separated under a pressure of about 10bars, flows into an extruder. The gases rising from the hopper arerecycled to the inlet of the first compressor.

The mixture of ethylene and α-olefin is introduced continuously into thereactor, into which the catalytic composition is also admitted. Theactivator TEA (25 mole %)-SILOXAL H₂ (75 mole %) was used in allexamples except for Example 86, in which a mixture of 15%TEA-85%-SILOXAL H₂ was used. The ratio Al/Ti(+V) was equal to 20. Thetemperature is regulated to the desired value while the pressure ismaintained at 800 bars for Examples 82 to 85 and 87 to 89, or 1200 barsfor Example 86. The copolymer collected after extrusion and granulationis weighed. The catalytic yield (R_(c)) is here expressed as kgcopolymer per gram-milliatom of titanium (or of titanium and vanadium,as necessary).

The following are determined for the copolymer obtained:

the melt index MI, measured according to standard ASTM D-1238 conditionE and expressed in dg/min.

the density d, measured according to standard ASTM D-792.

The conditions used and the results obtained are given in Table IV. Findicates the composition of the gaseous flow (% by weight each of themonomers), E ethylene, P propylene, B but-1-ene and M4-methylpent-1-ene. The catalytic composition used is referred to bymeans of the example describing its preparation. The polymerizationtemperature is expressed in ° C. H represents the level of hydrogen(transfer agent) as % by volume.

                  TABLE IV                                                        ______________________________________                                        Ex-                          Catalytic                                        am-  F (% by wt.)            composi-                                         ple  E     P     B   M   H    T    tion used                                                                            R.sub.c                                                                            MI   d                         ______________________________________                                        82   65    --    35  --  0.1  240  Ex. 30 25   3.7  0.928                     83   50    --    50  --  0.1  240  Ex. 30 22   5.7  0.925                     84   50    --    50  --  0.1  260  Ex. 30 12   16.4 0.923                     85   50    --    50  --  0.1  220  Ex. 31 29   1.3  0.927                     86   39    --    --  61  0.03 240  Ex. 37 11   2.2  0.926                     87   50    25    25  --  --   250  Ex. 39 10.5 8.9  0.905                     88   35    40    25  --  --   225  Ex. 39 12.5 8.8  0.882                     89   30    35    35  --  0.02 200  Ex. 37 14.6 1    0.891                     ______________________________________                                    

EXAMPLE 90 Determination of the Valency of Titanium in the TitaniumCompounds Obtained by Electrochemical Reduction

The following are subjected to analysis The reaction medium obtainedafter electrochemical oxido-reduction and containing the excess ofhalogenated solvent, and where required an inert solvent; theorgano-aluminum compound formed by oxidation; and the titanium (III)compound formed by reduction. The valency states of the titanium aredetermined by means of a three-part redox titration. The first stepallows the calculation of the content of Ti²⁺ +Ti³⁺. Ti²⁺ is oxidized toTi³⁺ by means of protons introduced in the form of a 2N solution of HClprepared with degassed distilled water. The Ti³⁺ formed, together withthe Ti³⁺ originally present, are then oxidized to Ti⁴⁺ by means of anexcess of a 0.2N solution of Fe³⁺. Fe³⁺ is reduced to Fe²⁺, which istitrated using potassium bichromate in a sulphuric-phosphoric acidmedium in the presence of 0.2% sodium diphenylaminesulphonate. Thequantity of Fe²⁺ thus determined corresponds to the Ti²⁺ +Ti³⁺ ionsoriginally present in the catalytic composition. The second step allowsthe content of 2Ti²⁺ +Ti³⁺ to be calculated. It consists in oxidizingTi²⁺ and Ti³⁺ by means of an excess of a solution of Fe³⁺ ions, in thepresence of protons to avoid the oxidation of Ti²⁺ to Ti³⁺, inaccordance with the reactions:

    Ti.sup.2+ +2Fe.sup.3+ →Ti.sup.4+ +2Fe.sup.2+ ; and

    Ti.sup.3+ +Fe.sup.3+ →Ti.sup.4+ +Fe.sup.2+

The Fe²⁺ ion is then titrated by means of potassium bichromate as above.The value obtained corresponds to the sum 2Ti²⁺ +Ti³⁺ present in thecatalytic composition. The third step allows the determination of thecontent of Ti⁴⁺ by reduction, by means of triethyl aluminum inaccordance with an atomic ratio Al/ Ti equal to 6, of the titanium (IV)present to titanium (III) and titanium (II). The titration is thencarried out in the same way as the first step above. The value of Ti²⁺+Ti³⁺ found corresponds to the sum Ti²⁺ +Ti³⁺ +Ti⁴⁺ of ions present inthe analyzed catalytic composition and to the total titanium content.The various percentages are calculated by solving the followingequations:

    Ti.sup.2+ +Ti.sup.3+ =A

    2Ti.sup.2+ +Ti.sup.3+ =B

    Ti.sup.2+ +Ti.sup.3+ +Ti.sup.4+ =C

Thus, the catalyst obtained in Example 12 contains 97.1% Ti(III), 1.8%Ti(II) and 1.1% titanium (IV). After storage for 2 months at ambienttemperature and protected from light, these contents became,respectively: 85.5%, 6.5% and 7.9%. The addition of butyl ethylmagnesium to the freshly prepared catalyst does not noticeably modifythe content of Ti(III) which is then found to be 96.6%.

Other embodiments of the invention will be apparent to one skilled inthe art from a consideration of the specification or with practice ofthe disclosed invention. It is intended that the specification andexamples be considered as exemplary only with the true scope and spiritof the invention indicated by the claims.

What is claimed is:
 1. A process for the preparation of a catalyticcomposition for the polymerization of olefins comprising:at leastpartial electrochemical oxidation of aluminum in a solvent of at leastone α,ω-dihalogenalkane, and simultaneously the electrochemicalreduction of a compound of titanium (IV).
 2. The process according toclaim 1, wherein the oxidation and reduction is carried out in thepresence of an inert solvent further comprising at least one saturatedaliphatic or cycloaliphatic hydrocarbon having from 6 to 14 carbonatoms.
 3. The process according to claim 1, wherein the oxidation andreduction is carried out in the presence of at least one α-olefin havingfrom 4 to 16 carbon atoms.
 4. The process according to claim 1, whereinthe titanium (IV) compound has the formula Ti(OR)_(n) X_(4-n), in whichX is a halogen, 0≦n≦4 and R is an alkyl radical having from 1 to 10carbon atoms.
 5. The process according to claim 1, wherein theconcentration of titanium (IV) compound in the reaction medium isbetween 20 and 600 millimoles per liter.
 6. The process according toclaim 1, further comprising adding to the reaction medium during thesimultaneous electrochemical oxidation and electrochemical reduction avanadium (IV) or vanadium (V) compound chosen from (i) the compounds ofgeneral formula VO(OR)_(m) X_(3-m), in which X is a halogen, R is analkyl radical having from 1 to 6 carbon atoms and 0≦m≦3, and (ii) thecompounds of formula VX₄, in which X is a halogen.
 7. The processaccording to claim 1, wherein the simultaneous electrochemical oxidationand electrochemical reduction are carried out by passing a quantity ofelectricity of between 1 and 12 Faradays per mole of titanium throughthe reaction medium.
 8. The process according to claim 7, wherein theelectricity is passed by use of an imposed cathodic potential of between-0.5 and -1 volt.
 9. The process according to claim 7, wherein theelectricity is passed by use of a regulated cathodic potential ofbetween 20 and 200 volts.
 10. The process according to claim 1, whereinthe simultaneous electrochemical oxidation and electrochemical reductiontake place in the presence of at least one magnesium halide.
 11. Theprocess according to claim 1, further comprising adding to the reactionmedium after the simultaneous electrochemical oxidation andelectrochemical reduction, at least one magnesium halide or at least oneorgano-magnesium derivative of formula R-Mg-R', in which R and R' arealkyl radicals, which may be identical or different, having from 1 to 12carbon atoms.
 12. The process according to claim 11, wherein themagnesium halide or the organo-magnesium derivative is used to obtain anatomic ratio Mg/Ti less than or equal to
 15. 13. The process accordingto claim 1, further comprising adding to the reaction medium after thesimultaneous electrochemical oxidation and electrochemical reduction, atleast one compound of vanadium (III), (IV) or (V).
 14. The processaccording to claim 13, wherein the compound of vanadium (III), (IV) or(V) is added to give an atomic ratio V/ Ti of up to 6.